1. Field of the Invention
The present invention relates to a vehicle air dryer and in particular to a vehicle air dryer desiccant cartridge.
2. Description of the Related Art
The provision of air drying apparatus, hereinafter referred to as an air dryer, in vehicle air systems is well known. The air dryer apparatus is typically positioned intermediate of the air source, for example a compressor, and a reservoir. The air dryer includes a desiccant material, for example a moisture adsorbing material such as silica gel, which removes moisture from the air supplied by the compressor so as to prevent said moisture being deposited downstream in the vehicle air system where it may over time damage components of the air system. So as to address the build up of moisture in the desiccant material the air dryer is periodically purged to atmosphere with dry air from the reservoir. Purging of the desiccant is typically undertaken during periods when the compressor is idle and no significant demands for dry air are being made of the reservoir. The desiccant material is typically provided in a removable canister, hereinafter referred to as a cartridge, which is releasably attached to the air dryer. The cartridge is periodically replaced so as to take into account reduction in the performance of the desiccant material over time.
It is not unknown for the air supplied by the compressor to include a mist of very fine oil droplets. The oil droplets are generated from the lubricating oil present in the compressor by the reciprocating action of the compressor. The oil mist typically passes through the air dryer and subsequently to the vehicle air system. Some oil mist will be deposited in the reservoir. While oil deposited in this manner is much less likely to damage air system components in the same manner as moisture, its deposit may lead over time to such problems as, for example, the constriction of narrow passageways in air system components and the degradation of elastomeric seals. It is an object of the present invention to provide an improved air dryer which seeks to prevent the transmission of oil therethrough.